-polyhedral-info -polly-check-parallel analyzes non parallel loop as parallel.

[llvmbot]

Bugzilla Link	36388
Version	unspecified
OS	Linux
Reporter	LLVM Bugzilla Contributor

Extended Description

The outer loop of the following program is analyzed as parallel by -polyhedral-info -polly-check-parallel. But the outerloop has loop-carried dependence and is analyzed as not parallel by -polly-parallel analysis.

float a[256],b[256]; float aa[256][256],bb[256][256],cc[256][256]; int main () { for (int i = 1; i < 256;i++) { a[i] = a[i-1]+b[i] ; for (int j=0;j<256;j++ ) { aa[i][j] = aa[i][j]+cc[i][j]; } } return 0; }

clang -O1 -S -emit-llvm -o loop.s loop.c opt -S -polly-canonicalize loop.s > loop.preopt.ll opt -polly-parallel -polly-ast -polyhedral-info -polly-check-parallel -analyze -q loop.preopt.ll -polly-process-unprofitable

Printing analysis 'Polly - Generate an AST from the SCoP (isl)' for region: 'for.body8 => for.cond.cleanup7' in function 'main': Printing analysis 'Polly - Generate an AST from the SCoP (isl)' for region: 'for.body => for.cond.cleanup' in function 'main': :: isl ast :: main :: %for.body---%for.cond.cleanup

if (1)

#pragma minimal dependence distance: 1
for (int c0 = 0; c0 <= 254; c0 += 1) {
  Stmt0(c0);
  #pragma simd
  #pragma known-parallel
  for (int c1 = 0; c1 <= 255; c1 += 1)
    Stmt1(c0, c1);
}

else { / original code / }

Printing analysis 'Polly - Generate an AST from the SCoP (isl)' for region: 'entry => ' in function 'main': Printing analysis 'Polly - Interface to polyhedral analysis engine' for function 'main': for.body: Loop is parallel. for.body8: Loop is parallel.

[llvmbot]

I think PolyhedralInfo::getScheduleForLoop is not working as expected for parallelism checking.